Observations

Description

Valves are linear with an inflation in the center of the valve and capitate to slightly capitate apices. The medial inflation of the valve is wider than the apices. Striae are usually parallel, but can be slightly radiate in the medial inflation. The striae are alternate. The axial area is narrow and linear. The central area is small and rhombic. Short marginal spines are present, although the spines are difficult to see in LM. The girdle bands are closed and have large septa. In addition to large septa, much smaller rudimentary septa can be observed in the girdle bands. The number of girdle bands varies per frustule; there can be any number from two to many. One rimoportula per valve is present, usually located near or within the central area. Cells are joined in colonies, usually in zig-zag or stellate formations. Frustules are rectangular in girdle view.

This taxon is highly variable in its morphology and its variability has been treated differently by different authors. Knudson (1952) described four varieties, based primarily on colony morphology. Koppen (1975), who many have followed for US taxonomy, separated T. flocculosa into three ‘strains’, based on size range and autecology. In Diatoms of the US, I include strains III, IIIp, and IV together in the concept of T. flocculosa.

For those interested in following Koppen (1975), strain III is distinguished by ends that are not distinctly capitate. The medial inflation widens gradually, usually to a width of 4.5-6.5 µm. Valves of strain III can be as long as 83 µm. Cells of strain III grow attached to surfaces, usually on rocks or macrophytes.

Strain IIIp appears nearly identical to strain III, except that valves can reach up to 122µm in length. Strain IIIp valves can also be slightly twisted. In addition, strain IIIp is planktonic.

Strain IV has capitate ends and the medial inflation widens abruptly to 7.5-8.5 µm. Strain IV is smaller than strain III, with a maximum length of 39 µm.

Valves with central valve inflation and capitate, to slightly capitate ends. The central inflation is wider than the terminal inflation. A hyaline area is present in the central valve. Marginal spines are present. A rimoportula is located near the central area. Regular and rudimentary septa are present on closed girdle bands.

Compare

Tabellaria fenestrata lacks marginal spines, has distinctly capitate apices and a narrow axial area, but no hyaline central area. The girdle bands in T. fenestrata are open and lack rudimentary septa.
Tabellaria flocculosa var. linearis is similiar to T. flocculosa in that they both have apices that are not distinctly capitate. In both species, there is a narrow axial area. However, in T. flocculosa var. linearis, apices are as wide, or wider, than the central inflation. There is no hyaline central area in T. flocculosa var. linearis. Rudimentary septa may be present.

According to Koppen (1975) Tabellaria quadriseptata lacks distinguishing characters from T. flocculosa, and they should be considered conspecific.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

NCBI Genbank Taxonomy

North American Diatom Ecological Database (NADED)

NADED ID: 67004

Autecology Discussion

Tabellaria flocculosa var. flocculosa tends to grow in freshwater, slightly acidic to acidic waters, though it can have a wide pH tolerance (Hustedt 1930, Niels 1981, Round, Crawford and Mann 1990, Krammer and Lange-Bertalot 1991). It is commonly found in peat bogs, running water, or lakes. T. flocculosa is cosmopolitan and more common in northern latitudes (temperate to arctic regions).
Strains III and IV grow attached to hard substrates or vegetation, while Strain IIIp is planktonic. Strains III and IV grow in zig-zag colonies of indeterminate length. Strain IIIp can grow in zig-zag or stellate colonies, but usually no more than 5 cells per colony.

Habits

Size Range

11-100 µm3 (ie Achnanthidium)
101-1000 µm3 (ie Amphora veneta)

Motility

non motile

Attachment

unattached
prostrate (e.g. mucilage pad)

Habitat

benthic
planktonic

Colony

colonies common

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Tabellaria flocculosa

Distribution

The distribution map represents the relative abundance of this Tabellaria flocculosa in the western EMAP study. Relative abundance is a measure of the proportion of cells of this species based on a "fixed count" of 300 total diatom cells counted and identified. Each of the western EMAP sample sites is shown, either with a black dot for sites where Tabellaria flocculosa was not recorded, or with a red circle indicating the relative abundance of Tabellaria flocculosa.

Note that the size of the proportional symbols varies between species to help show both abundant and rare species.

Scale for the map to the left

EMAP Response Plots

Tabellaria flocculosa

Responses

The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Tabellaria flocculosa from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)STRAHLER = distribution plot of the Strahler Stream Order SLOPE = stream reach gradient (degrees)W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.PHSTVL = pH measured in a sealed syringe sample (pH units)log_COND = log concentration of specific conductivity (µS/cm)log_PTL = log concentration of total phosphorus (µg/L)log_NO3 = log concentration of nitrate (µeq/L)log_DOC = log concentration of dissolved organic carbon (mg/L)log_SIO2 = log concentration of silicon (mg/L)log_NA = log concentration of sodium (µeq/L)log_HCO3 = log concentration of the bicarbonate ion (µeq/L)EMBED = percent of the stream substrate that is embedded by sand and fine sedimentlog_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.